Electronics > Projects, Designs, and Technical Stuff
Constant-power output into load with varying impedance
(1/1)
KaneTW:
I'm using a DRV8412 to drive a RLC load at resonance (so it appears like a resistive load) with a fundamental of 40-100kHz. Originally when I chose that IC, I expected the maximum load impedance to be around 20-25 Ohm. However, it appears that depending on load conditions, it can vary between 10-50 Ohm.

I've considered using a step-up transformer, but that pushes too much current through the IC at low impedance. Switching 1:1/step-up might be reasonable (e.g. using a Coilcraft configurable transformer), but sounds like a headache to get right.

Other options I'm thinking of is redesigning with external FETs (thankfully I'm just using an EVM right now). Using resonance to add gain doesn't work due to my bandwidth requirements.

Any other ideas?
Marco:
Feed the rails for the DRV8412 with a constant frequency constant duty cycle boost converter.
KaneTW:
I'm already driving it at the highest DC voltage it recommends (50V), which after selective harmonic elimination and filtering drops down to just about 50V/sqrt(2) RMS, and I need a 60W output. It has an absolute maximum rating of 70V, but that's for transients only.

I need to measure the load impedance under real life conditions; if it's more constrained than 10-50 this might be more feasible. Otherwise I'm thinking GaNFET (due to low RDSon and switching losses) at 80V nominal should work and improve efficiency a bit more.
Loses the low-effort benefit of the DRV84x2, though.

I can already adjust the output RMS by changing the modulation, so a down-regulating the rails voltage won't help. A 1:1.5 step-up might just be good enough if I can accept a slightly reduced full-power range. Efficiency drops to about 92% simulated though (down from 96%) due to the high current through the switches.
Navigation
Message Index
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod